The present invention relates to protective devices for liquid and gas conducting systems, such as hydraulic systems, especially to so-called hose rupture valves, the invention relating to an improvement on the valve arrangement described in U.S. Pat. No. 4,004,607.
In this patent there is described a valve arrangement for protecting a conduit system against unintentional pressure variations, such as occur when the hose or conduit is ruptured, the arrangement being introduced into especially exposed conduit sections in the system, e.g. a flexible hose incorporated therein. The valve arrangement comprises a blocking valve arranged at the inlet of the conduit section, this valve being kept open during normal operation, and a flow-sensing means arranged at the outlet of the conduit section, of the pressure drop type, e.g. an orifice plate or venturi constriction. The flowing medium produces a pressure drop, in a normal way, across the flow sensing means, and via an auxiliary or pilot conduit the pressure drop is transferred to the inlet of the conduit section, to be there compared with the pressure drop which the flowing medium causes over the valve itself. As long as the relationship between both pressure drops is kept at a generally constant, predetermined value, i.e. as long as the volume flow through the sensing means is the same as through the blocking valve, the latter is kept open. However, if a rupture or leak occurs in the monitored conduit section, the volume flow through the sensing means lessens which is reflected by the pressure drop across it becoming less. The relationship between both pressure drops will thus no longer be the same, and the deviation from the constant value is registered by a pressure-comparing valve means, arranged to cause immediate closure of the blocking valve if the deviation exceeds a predetermined value. In the preferred case the pressure-comparing valve means consists of the blocking valve member itself, which is formed as a slide, movable between an open position and a closed position. The pressure drop or differential pressure across the orifice plate or venturi constriction is hereby arranged to actuate the slide in one direction while the pressure drop or differential pressure across the blocking valve which drop, in fact, appears across the slide itself, is caused to actuate the slide in a reverse direction, the arrangement being such that the slide is urged towards closure and blocks the flow through the valve if the said alteration in the pressure drop ratio occurs.
This known valve arrangement is extremely reliable operationally and functions with high selectivity, i.e. it reacts only for rupture and leaks, not for flow surges or pressure waves occurring during normal operation. Practical experience has however shown that improvements are desirable in especially two respects. In the first place, the valve arrangement should give as little flow resistance as possible for a flow in the reverse direction, i.e. flow from the outlet to the inlet of the monitored section, a relationship which is of importance in the use of the valve arrangement on hydraulic working machines, e.g. excavating machines. In the second place there is the general desire to reduce the dimensions of the apparatus and to simplify the components thereof.
The invention thus has the object of providing a valve arrangement of the kind in question which satisfies the desires mentioned above. This is achieved, and a valve arrangement especially suitable as a hose rupture valve or holding valve is provided by the apparatus according to the invention being given the characterizing features disclosed in the claims.